1. Field of the Invention
The present invention relates generally to a monitor. In particular, the present invention relates to a self-test device for a monitor which can self-test whether the monitor is in a normal operating state or not in case that a color picture is not displayed or is abnormally displayed on the screen of the monitor connected to a personal computer.
2. Description of the Related Art
Generally, a monitor has a self-test function whereby a prescribed picture for self-test is displayed on the screen so that a user can check the normal or abnormal state of the monitor by viewing the displayed picture if the user disconnect a cable connector of the monitor from the personal computer (PC) in case that a color picture is not displayed or is abnormally displayed on the screen of the monitor connected to the PC.
The conventional self-test circuit of a monitor, as shown in FIGS. 1 and 2, includes a cable connector 2 for connecting the monitor to a signal output section 1 of the PC, a display power management (DPM) section 3, connected to a self-test terminal ST of the cable connector 2, for performing a display power management function, a DPM control section 4 for receiving a self-test signal provided through the cable connector 2 and controlling the DPM section 3 according to the self-test signal, a video amplifying section 5, connected to red (R), green (G), blue (B) terminals of the cable connector 2, for amplifying R,G,B video signals inputted through the R,G,B terminals of the cable connector 2, and a video output section 6 for outputting the R,G,B video signals amplified by the video amplifying section 5 to display the outputted R,G,B video signals on the screen of the monitor.
In FIG. 2, the reference numeral B.sup.+ denotes a DC supply voltage, 5A denotes a video amplifier, R1 to R10 denote resistors, C1 to C3 denote capacitors, Q1 to Q5 denote transistors, L1 to L4 denote coils, D1 denotes a diode, and LD1 and LD2 denote light emitting diodes (LEDs).
The operation of the conventional self-test circuit as constructed above will be explained.
Referring to FIGS. 1 and 2, in a state that the signal output section 1 of the PC is connected to the cable connector 2 of the monitor, the self-test terminal ST of the cable connector 2 becomes in electric contact with the signal output section 1 of the PC which is connected to ground. Accordingly, the video signal outputted from the PC is transferred to the monitor and then displayed on the screen of the monitor.
At this time, if a suspend/standby signal of a `high` level is outputted from the DPM control section 4 which is connected to the self-test terminal ST of the cable connector, the transistors Q2 and Q3 in the DPM section 3 are turned on, causing the red LED LD1 to be turned off, while the green LED LD2 is turned on. Meanwhile, if the suspend/standby signal of a `low` level is outputted from the DPM control section 4 when no video signal is displayed on the monitor screen, the transistors Q2 and Q3 are turned off, causing both the red and green LEDs LD1 and LD2 to be turned on, resulting in that the two LEDs LD1 and LD2, as a whole, display an umber color which is the combination of the red and green colors.
For instance, since the suspend/standby signal outputted from the DPM control section 4 becomes `low` and thus the LEDs LD1 and LD2 display the umber color during the display power management (DPM) operation of the monitor, a user can recognize that the monitor is now performing the DPM function by viewing the displayed color of the LEDs LD1 and LD2.
If the cable connector 2 of the monitor is disconnected from the signal output section 1 of the PC in the normal operating state of the monitor as described above, the self-test terminal ST of the cable connector 2 is floated, causing the transistor Q1 in the DPM section 3 to be turned on. At this time, no video signal is displayed on the screen of the monitor. Also, the DPM function is not performed, and only the green LED LD2 is turned on.
In the conventional monitor which does not employ a microprocessor IC or an on-screen display (OSD) function, however, the DPM function is performed utilizing the self-test signal ST though the cable connector 2 of the monitor is disconnected from the signal output section 1 of the PC. Accordingly, a self-test pattern cannot be displayed on the monitor screen, and thus the user cannot check the normal or abnormal operating state of the monitor.